The number of deals offered by 31 major department stores and apparel retailers increased 63 percent between 2009 and 2012, and the average discount jumped to 36 percent from 25 percent, according to Savings.com, which tracks online coupons.

But the Black Friday secret some stores do not want customers to know: They may not be getting the deal they think they are.

"Stores set their prices so that when they do discount, they can still make a profit," Prabhakar said. "That whole pricing system where they mark up their products just so they can discount is [built] into their business model."

1. The 30 percent rule. As a general rule of thumb, shoppers should look for discounts at 30 percent or more. Most stores expect to sell items at 30 percent off, so look for discounts higher than that - those are the real deals.